Once thepower into the thermoelectric is determined, Equations 1 and 2 can be used tosolve for T h and to determine whether the original estimate of T h was appropriate. The input power to the thermoelectric, Pin, is the product of the currentand the voltage. Using the 3. The calculated T h is close enough to the original estimate of T h ,to conclude that the CP1. If an exact solution needs to be known, the process of solving forT h mathematically can be repeated until the value of T h does not change.
The material used for the assembly components deserves careful thought. Theheat sink and cold side mounting surface should be made out of materials thathave a high thermal conductivity i. However, insulation and assembly hardware should be made of materialsthat have low thermal conductivity i. Environmental concerns such as humidity and condensation on the cold sidecan be alleviated by using proper sealing methods.
A perimeter seal Figure 4 protects the couples from contact with water or gases, eliminating corrosion andthermal and electrical shorts that can damage the thermoelectric module.
Figure 4: Typical thermoelectric from Melcorwith a perimeter seal. Given the hot side temperature, the cold side temperature and the heat load,a suitable thermoelectric can be chosen. A multistagethermoelectric achieves a high T by stacking as many assix or seven single stage thermoelectrics on top of each other. Although there is a variety of applications that use thermoelectric devices,all of them are based on the same principle. When designing a thermoelectricapplication, it is important that all of the relevant electrical and thermalparameters be incorporated into the design process.
Once these factors areconsidered, a suitable thermoelectric device can be selected based on theguidelines presented in this article. Levine, M. Melcor Corporation, Thermoelectric Handbook, Sept. Rowe, D. Figure 1: Cross Section of a Typical TECouple Introduction Thermoelectric coolers are solid state heat pumps used in applications wheretemperature stabilization, temperature cycling, or cooling below ambient arerequired.
How the Thermoelectric Works. Thermal Parameters Needed The appropriate thermoelectric for an application, depends on at least threeparameters. This is because you need to add more ceramic plates to cover a larger area, and this will require higher input voltage to operate.
The more ceramic plates you have, the more electricity you'll need to use to run the machine, whereas a slightly larger compressor doesn't use that much more electricity than a smaller one. Thermoelectric cooling is entirely dependent on the ambient temperature for its ability to cool. Unlike a compressor system, which can maintain sub-freezing temperatures in certain applications, a thermoelectric device can only bring down the temperature to a certain point below room temperature. That means that if it's 65 degrees outside, and your TEC can bring down temperatures by 30 degrees, you can achieve a low temperature of 35 degrees.
But when summer rolls around and the mercury rises, your cooling capacity rises with it. On a degree day, the cooler will only be able to hover around 65 degrees. This may not be a problem indoors if you have central heating and air conditioning to limit extremes, but the temperature difference can be a big deal in RVs or camping applications.
While thermoelectric cooling does offer fine temperature control, it's crucial to understand that this is only within the range allowed by the outside temperature on any given day.
Thermoelectric coolers also don't dehumidify the air around them. The ceramic plates simply transfer heat away from one area and into another, leaving the moisture content of the air intact.
This is very different from compressor cooling, in which cold evaporators on the inside of the machine lower the dew point of the air and cause moisture to condense.
These water droplets are carried outside and left to drip away in a compressor air conditioner, effectively lowering the moisture content of the air in your home.
It should be noted that dehumidifying may or may not be a virtue depending on the application; for example, cigar humidors should stay quite moist as they cool, while a refrigerator for food should be dry to help keep rot at bay.
Most people don't build their own electronics, so thermoelectric cooling typically comes into play in small refrigerators or portable coolers for food and drink. So which is better when it comes to choosing a dedicated wine fridge or beverage fridge? Thermoelectric cooling is a fascinating technology, and it definitely has its place when it comes to wine coolers and humidors.
Be sure to carefully compare your options as you shop and keep in mind the features you personally find most important to select the perfect appliance for your home.
One application where a thermoelectric cooler is always a good choice? A high-performance cigar humidor. This is because the Peltier effect doesn't have any influence over the humidity levels in your humidor, making it much easier to keep humidity levels where you like them — without having to constantly add moisture to keep up with a compressor's dehumidification.
If you live in a cold climate, a thermoelectric cooler can also be run in reverse, which will allow it to operate as a heater to maintain the perfect temperatures for your cigars all year round. The first important discovery relating to thermoelectricity occurred in when a German scientist, Thomas Seebeck, found that an electric current would flow continuously in a closed circuit made up of two dissimilar metals provided that the junctions of the metals were maintained at two different temperatures.
Seebeck did not actually comprehend the scientific basis for his discovery, however, and falsely assumed that flowing heat produced the same effect as flowing electric current. Twenty years later, William Thomson eventually known as Lord Kelvin issued a comprehensive explanation of the Seebeck and Peltier Effects and described their interrelationship.
At the time, however, these phenomena were still considered to be mere laboratory curiosities and were without practical application. This Russian interest in thermoelectricity eventually caught the attention of the rest of the world and inspired the development of practical thermoelectric modules. Without going into too much detail, we will examine some of these fundamental thermoelectric effects.
The thermocouple conductors are two dissimilar metals denoted as Material x and Material y. Thermocouple B is used to measure the temperature of interest Th which, in this example, is higher than temperature Tc. With heat applied to thermocouple B, a voltage will appear across terminals Tl and T2. The heat sink inside helps to cool the food, sucking heat out of it and conducting it into the thermopile. Thermoelectric cooling is not very efficient. It is often only about 10 percent efficient, compared to normal refrigeration, which is in the 40 to 60 percent range.
Normal refrigeration isn't practical for a cooler, since it is heavy, bulky and overpowered. But the thermoelectric cooler doesn't have to do that much. The refrigerator is insulated, so not much heat leaks in.
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